Flickr/Lwp KommunikációMost people think polygraphs — also called lie-detector tests — can determine whether you're lying. But the technology has its critics.

"The public needs to know that polygraph testing has no scientific basis and is inherently biased against truthful people, yet liars can train themselves to pass," said George Maschke, the co-creator of Antipolygraph.org.

Maschke, whose website aims to expose the test's shortcomings, told Business Insider that just one insight could have a huge impact on a person's results: Examiners expect takers to lie on certain questions, known as control or comparison questions.

These "control questions" include harmless accusations that most people wouldn't admit to, such as "Have you ever lied to get out of trouble?" or "Have you ever taken supplies from work?"

According to Maschke, if people think about certain things when answering these control questions, the test becomes easier to pass.

Polygraphs work by monitoring three physical reactions: sweat, using electrodes attached to the fingers; heart rate and blood pressure through an arm cuff; and breathing through chest straps. Any changes in those factors cause needles making lines on a paper to rise and fall. Examiners then analyze these patterns to determine the probability someone is telling the truth or lying.

But the name "lie detector" is a "term of convenience, not science," Raymond Nelson, president of the American Polygraph Association, a trade group representing polygraph examiners, told Business Insider.

That's because polygraphs don't actually measure lies, Nelson writes in a commentary called "The Scientific Basis for Polygraph Testing," published in the polygraph association's journal Polygraph. Instead, Nelson writes, polygraphs measure the differences between how truthful people react to relevant questions and control questions and how deceptive people react to those questions.

And there's a complicated process for analyzing the results, Nelson said. Examiners compare a person's answers to relevant questions with the control questions they're expected to lie about. It's a similar idea to testing students at the beginning of the school year and the end to measure their progress, Nelson said. Based on these comparisons, examiners then use statistical analysis to determine the probability that the test taker is lying.

While polygraphs are most often used in criminal investigations, certain government agencies can require one as part of the application process. For example, if somebody is interviewing for a position related to national security, such as with the FBI or CIA, the examiner might ask if anyone instructed the taker to seek employment there, Maschke said.

Maschke would know about the FBI's protocol for polygraph tests; he says he wrongly failed an FBI polygraph in 1995 when he applied to be a translator. While the FBI told Business Insider we would have to file a Freedom of Information Act request to obtain Maschke's records, his website refers to an FBI HQ file released to him in 2001.

An intense question about spying, however, could cause even a truthful person to react badly.

"Any time I present a stimulus, I'm always going to get a response," Nelson said. "So how do we measure a response to a neutral question — like 'Is it Tuesday?' — compared to a relevant question — like 'Did you do the bad thing?' whatever the bad thing is."

To attempt to figure out whether somebody is lying, the examiner would compare the taker's reaction to a relevant question with the reaction to the control question. Overly simplified, if the taker reacts more to the control question than to the relevant question, the person is probably telling the truth.

Aside from expecting a less than truthful answer, examiners sometimes also steer the taker into lying — a technique called the "probable-lie comparison."

"They might preface the question with an explanation that the sort of person who would lie to get out of trouble is the sort of person who might commit espionage," Maschke said. "They want the person to make a blanket denial."

Some people, however, answer control questions honestly and might not show a strong reaction. That's why Maschke accuses polygraph tests of actually punishing the truthful.

"The more admissions you make [during the control] and the more relaxed and comfortable you feel, then perversely the more likely you are to fail," he said. "To protect yourself against a false positive outcome ... you want to augment your response to that control question."

The American Polygraph Association, however, notes that examiners will offer the taker an opportunity to explain unusual reactions when appropriate. Most jurisdictions, including the government, have also forgone the use of probable-lie comparison, Nelson said, and now rely on "directed lie comparison," which doesn't require any manipulation when asking control questions.

While polygraphs include sensors and statistical algorithms to weed out the fakers, "there's no test in the world that doesn't have some vulnerability to faking," Nelson acknowledged.

In 2002, the National Academy of Sciences published one of the most comprehensive studies of polygraph accuracy, concluding that while the tests could "differentiate lying from telling the truth at rates well above chance," they weren't accurate enough for security purposes.

"That's still better than any other technology available today," Nelson told NPR. The association puts the test's accuracy above 80%. Regardless of the questions surrounding its accuracy, polygraph testing remains legal at federal and state levels. The Employee Polygraph Protection Act, however, does prohibit most private employers from using them during interview processes or employment.

"I'm actually not at all interested in helping people pass polygraphs who are not qualified for government jobs or helping criminals evade justice," Maschke said. "People just need to protect themselves against the false positives."

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